Human drug addiction is associated with staggering personal and societal costs. It's thought that the persistence of drug craving and the risk of relapse involve long-lasting changes in neural gene expression arising through a number of transcriptional and epigenetic mechanisms. It's also known that midbrain dopamine (DA)-synthesizing neurons play an important role in both the positive and negative reinforcing features of drug abuse, providing a compelling rationale for identifying drug-induced molecular changes arising within these cells. Yet, remarkably, in contrast to the intensive study of targets of DA signaling, we have but a fragmentary understanding of the molecular consequences of chronic drug exposure on DA neurons themselves. The study of postmortem brains from human drug abusers should provide an valuable window through which we can examine the pathophysiology of addiction and evaluate the molecular concordance between human drug abuse and animal models- a salient point given some important differences in the manner in which people abuse drugs and the anatomical substrates upon which those drugs act. Unfortunately, postmortem human studies have lagged behind other areas of drug abuse research. This proposal will tap into the promise of postmortem studies to address critical gaps in our knowledge regarding human addiction, DA neurons, and epigenetics. Microarray analysis will identify changes in midbrain gene expression associated with chronic cocaine abuse, determining the biological processes most impacted and the statistical performance of robustly changed transcripts as biomarkers diagnostic for this disorder. Subsequent experiments will determine the extent to which these key changes generalize to other drug abusing cohorts (to address potential commonalities of addiction mechanisms), as well as how cocaine abuse modifies the known age-vulnerability of DA neurons- questions warranting serious consideration given the increasing prevalence of opioid abuse and poly-drug abuse, including drug abuse among older adults. Final experiments will investigate the role of specific epigenetic mechanisms (e.g., DNA methylation and long noncoding RNAs) in mediating the chronic effects of cocaine abuse. These studies will provide important new insights into the molecular pathophysiology of human drug addiction and should facilitate the development of new therapeutic strategies.